Loaded signaling conductor



.E BT T LOADED SIGNALING CONDUCTOR Original Filed March 5, 1924 CURRENT a '2 2 a a .05 .IO J5 C UPPENT DISM/VCE/N AMI/7S mom f5; 0F :zanpmmmm H515 I IlIIlIlIl/llmwllllllnlm lNl/ENTDP JaH/VJQLBERT ATTORNEY Patented June 1930 UNITED JOHNJ. GILBERT, or DoUGLAsTon; ew roux, ASSIGNOR T0 WESTERNELECTBIQC' GOMIPANY, INCORPORATED, or New YORK, n. an, A cpRroRATIoN on E YORK j LOADED. SIGNALING connuo'ron Originalapplication. filed. March 5,1924, Serial No. 696,981, and' in France January 6, 1924. 2 Divided and this application filed May 31, 1928 ScriaI'No. 281,617.

duce signal distortion which results from variations m-the 1m' edance of the conductor with variations in through. i V

Inlong submarme cables the overall attent m current flowingtherenation is so great that relatively large cur-. rents must be applied at one end 1n order that signals of suitable strength may be received at the distant end. If the conductor is loaded with magnetic material the permeability and hysteresis losses of which vary with themagnetizin force, the large variations the current an hence the magnetlz lng force 1n the terminal sections may cause thef mductance and resistance due to the loading material to vary between widewlimits. As aresult of these variations in the inductance and resistance of the conductor, it is difiicu'lt to construct an artificial line that will simulate such a cable with suflicient exactnessf'or duplex telegraph operation. If the cable is designed for telephone or carrier frequency operation there is the. additional objection that the varying impedance produces inter-' modulation between different telephone and carrier I frequencies with result ant distortion. It 1s proposed, lnaccordance with th s 111- ventlon to reduce the variat ons in inductance and in efiective impedance ofthe terminal sections'of a loaded conductor by'reducing the amount of theloading materialon'tho'se sections as compared to the loadin'g'on the sections of conductor more remotejtrom the.

terminals. I

This is a continuation as to certain divisible v 1 subject matter. "of J J. Gilbert applications Serial No. 696,981-,ffiled March 5, .1924, and

Ser. No; 579,393, filed Aug. 3, 1922.

The invention will now be explained in connection withthe drenvin'g in which;

"Fig. 1 comprisescurves indicating the variations in the inductance and resistance of. a loaded conductor with variations inl'the This invention relates to long loaded-sub-- signalinglcurrentinv a conductor at various points along 'its'length';

, Fig.3 is a diagrammatic showing of how, the loading may .be tapered on a conductor in a duplex telegraph system and p .Figs. e and 5 disclose methods of reducing: p the; amount of loaclinglnaterial on thevter minal portions of the conductor.

"It has long been recognized that loadinga s gnal ng conductor with magnetic mater al 1 will in "eneral decrease the attenuation due to the distributed resistanceand capacity ot the conductor.

Objectionable characteristic s may; how-i ever, result from the loadingitselfl For instancethere is always introduced a certain amount of dissipation due to eddy current These lossesare the more objection. 9

Likewise the permeability of theloading Ina-1 '7 terialvarieswith the current. Hence, whereas an unloaded conductor may have substan.

t'ially'constant resistance and inductance for. all intens ties of current thatflmay be trans-: mltted thereover, the eflect ve res stance and inductance vof loadedconductor may i 1 crease rapidly with an increase in' current'. These variations lnthe flinductance and effective resistance of a loaded conductor when traversed bycurrents-of difierent intensities areof course dlfierentln degree for dlfierent loading mater als, The variatlons "in a conductor loa'ded'witha particular alloy containing about 80% nickel and the balance chiefly iron when heat treated to give arhigh Initial permeability are shown in of the drawing.

On a telegraph cable operated duplex these characteristics'iof a loaded cable become -particularly objectionable because .it is very diflicult and expensive .tofbuild. an artificial line that will have the 'same' variable resistance and inductance. characteristics astlie loaded variations with' thej current variations are ob- :ss :cable. Ona't'elephoiieconduct0r impedance jectionable because they produce intermodulation ofthe different frequency; waves co nprising the speech spectrum or different dicates that the current is reduced to less than teristics'resulting from loading would originate on the terminal sections only of a conductor. This is because the transmitted currents are rapidly attenuated and after traversing a length of conductor which may be a relatively small fraction of the total length they are reduced to such values that the va *riations in impedance resulting therefrom become negligibly small. The relative magnitudes of the currents in a typical submarine cable at various points along its length are shown in the curve of Flg. 2. Thls curve 1nhalf its original amplitude at a point about 200 nautical miles from the terminal and that at a distance of 500 miles the current is reduced to value at which, referring to Fig. 1,

the variations in the resistance and inductance of the loaded conductor may be neglected.

Since it is in the terminal portions only of a loaded cable that the objectionable characteristics of the loading arise, those portions of the conductor may be modified by making such changes as are necessary in the loading to reduce the variations in impedance, w1th,

out materially increasing the desirable low overall attenuation due to the normal loading on the main portion of the cable.

There are severalmethods of reducing the impedance variations on the terminal sections. The simplest of course is to remove all *the loading material andthis may be desirable in some instances.

The preferred, method in'accordance with this invention, however, is to merely reduce the amount of the loading material on the terminal sections. This may be done by successive reductions in the amount of material at 'dlfferent distances from the terminal.

Thus, as shown in Fig. 3 only a very thin layer of loading material may be used on the first sectionof the cable and the thickness of loading material increased on second, third and fourth sections until the fourth or central section is fully loaded. Fig. 3 discloses a cable arranged for duplex operation and in such a system the terminal sections having different degrees of loading are balanced by sections of. artificial line having correspondingly different inductance and resistance characteristics.

The amount of loading material may be reduced in several ways. Where the material is applied to the conductor in the form of a single helical wrapping of tape or wire, the thickness of the tape or wire may be reduced. An alternative method, shown in Fig; 4:, is to increase the space between successive turns. When the normal loading on the center portion of the cable is in two or more layers, the

number of layers may be reduced on the terminal sections as shown in Fig. 5. Of course an alternative method is to reduce the thickness of the tapes without reducin the number of layers or to reduce both the thickness and the number of layers.

WVays of reducing the amount of loading material on the terminal section other than those suggested may of course be utilized. For instance the terminal section might be made up of alternate lengths of loaded and unloaded conductors, each length of conductor being short as compared to the length of the waves to be transmitted.

In general the reduction in resistance variations due to lighter loading is explained by the fact that the hysteresis losses are directly proportional to the amountof magnetic material employed. The impedance variations due to changes in the inductance are also less because the maximum inductance is reduced and the magnitude of the variations vary, to a limited extent at least, with the maximum values.

lVhat is claimed is:

1.. inductively loaded signaling conductor having great overall attenuation and having continuously loaded sections in which the amount of the loading material per unit length of conductor is less on a section of said conduct-or adjacent an end thereof than on a section of said conductor more remote from the end.

2. A 'loaded, signaling conductor having great overall attenuation and having continuously loaded sections, the quantity of loading material per unit length being relatively large in a portion of the conductors where the signaling current is small due to its having been attenuated by passage through a portion of the conductor and being relatively small in a part in which the signaling current is large.

. 3. A long submarine cable comprising a conductor surrounded by one or more helical wrappings of magnetic material, characterized-in this that the thickness of said wrappings on a section of said cable adjacent an end thereof is less than the'thickness of the wrappings on a section more remote from the end: i

4. A submarine cable in which a section near a terminal thereof and a section near the center thereof are loaded withmagnetic mater al, the loading being such that the flux density in the loading material produced by a given small current traversing the first its named section is the same as, but the total flux is less than, that produced in the loading material by an equal current traversing the second named section.

In Witness whereof, I hereunto subscribe my name this 29th day of May, 1928.

JOHN J. GILBERT. 

